Typical prior art demand water pressure maintenance systems monitor the pressure with a pressure switch. When the pressure drops below a selected level, the switch activates relays or acts directly to a pump that raises the pressure of the water. When the pressure reaches a higher selected level, the switch opens and cuts off power to the pump. In order to keep the switch and pump from rapidly cycling on and off, the turn on pressure is usually selected to be 20 to 30 psi below the turn off pressure. This is usually achieved in the art with a single mechanical switch that can be set to turn on and off at different pressures. However, since water is essentially incompressible, even a small amount of pumping quickly eliminates the 20 to 30 psi difference so that the switch and pump will still cycle on and off very fast. This could burn up the switch contacts and the pump motor. Hence, prior art water systems must use an accumulator tank into which the pressurized water flows and compresses a compressible gas such as air. In this way, the pump motor stays on longer while the air is compressed in the accumulator tank. After the pump turns off, it remains off for a longer time while the compressed air in the accumulator sustains pressure in the water system. It would be nice to eliminate the need for this accumulator tank which is expensive, heavy, and space consuming, especially a problem for water pressure systems installed in boats, recreational vehicles, and the like.
Another prior art problem is that the selected high pressure turn off point must be kept well below the maximum capability of the pump to take into account manufacturing tolerances in the pressure switch and possible voltage variations. Thus, the full capacity of the pump is never realized, which is inefficient. Also, the on and off pressure settings are closer together so that, once again, cycling of the switch and pump is increased. The present invention avoids these problems with a control system that does not need an accumulator tank and makes available the full pumping capability of the pump.